The current study has two objectives: 1) to examine situational, trait, informant, method, and temporal variation as they relate to childhood behavior disorders; and 2) to replicate, in a prospective manner, previous findings obtained by the current research group concerning the differential concurrent and predictive validities of the traits of hyperactivity and aggression. The situations under investigation include the home, school, and a clinic playroom; the traits to be measured include hyperactivity, aggression, and inattention; the informants include the parents, teacher, child, classmate peer, and examining clinician; and the methods include rating scales, psychological tests, and classroom and playroom observtions. Fifty outpatient male referrals to the Child Psychiatry Department and 35 classmate controls will be seen for each of two years, and each child will be followed up two years later. A symmetrical design will be employed in which both parents and child will be rating both parent and child behaviors on comparable instruments, as will the teacher, classmate peer, and child. Multivariate analyses will be used to reveal the relative roles played by situational, trait, source, method, and temporal factors in the classification of childhood behavior disorders.